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Lassa Fever Article: ***Note that bold regions are from the original article, and non-bold words are additions in places where they would be best suited for the article.

Introduction:

The Lassa virus is a member of the Arenaviridae virus family. This virus is an old world arenavirus, which can be described as enveloped, single-stranded, and bi-segmented RNA. This virus has a both a large and a small genome section, with four lineages identified to date: Josiah (Sierra Leone), GA391 (Nigeria), LP (Nigeria) and strain AV.

Diagnosis:

A range of laboratory investigations are performed, where possible, to diagnose the disease and assess its course and complications. The confidence of a diagnosis for Lassa Fever can be compromised by several factors if laboratory tests are not available. One comprising factor is the number of febrile illnesses present in Africa, such as malaria or typhoid fever that could potentially exhibit similar symptoms, particularly for non-specific manifestations of Lassa fever. Misdiagnosis is frequently a concern especially i'''n cases with abdominal pain. In countries where Lassa is common, Lassa fever is often misdiagnosed as appendicitis and intussusception which delays treatment with the antiviral ribavirin. In West Africa, where Lassa is most prevalent, it is difficult for doctors to diagnose due to the absence of proper equipment to preform tests.''' The FDA has yet to approve a widely validated laboratory test for Lassa, but there are tests that have been able to provide definitive proof of the presence of the LASV virus. These tests include cell cultures, PCR, ELISA antigen assays, plaque neutralization assays, and immunofluorescence essays. However, immunofluorescence essays provide less definitive proof of Lassa infection specifically. '''An ELISA test for antigen and IgM antibodies give 88% sensitivity and 90% specificity for the presence of the infection. Other laboratory findings in Lassa fever include lymphopenia (low white blood cell count), thrombocytopenia (low platelets), and elevated aspartate aminotransferase levels in the blood. Lassa fever virus can also be found in cerebrospinal fluid.'''

Epidemiology:

The spread of the virus is due primarily to the nature of the Lassa virus host. The Multimammate rat can quickly produce a large number of offspring, tends to colonize human settlements increasing the risk of rodent-human contact, and is found throughout the west, central and eastern parts of the African continent. Once the rat has become a carrier, it will excrete the virus throughout the rest of its lifetime through feces and urine creating ample opportunity for exposure. This rat is also a known food source in West Africa, and hunting and consuming an infected rat increases the risk of infection for those individuals.

Research has indicated the number of individuals infected by Lassa range anywhere from 100,000 to 300,000 up to two or three million people annually, with up to 5,000 deaths per year in West Africa alone '''. We need the CDC page cited here as well''' In certain areas such as Sierra Leone and Liberia, 10-16% of admitted patients have the virus. Also CDC here too please. The case fatality rate for those who are hospitalized for the disease is about 15-20%. Research in Guinea showed a twofold increase risk of infection for those living in close proximity to someone with infection symptoms within the last year.

Lassa has been linked to high risk areas near the western and eastern extremes of West Africa. These areas cannot be well defined by any known biogeographical or environmental breaks . However, it is relatively common in parts of West Africa where the multimammate rat is found, '''particularly Guinea (Kindia, Faranah and Nzerekore regions), Liberia (mostly in Lofa, Bong, and Nimba counties), Nigeria and Sierra Leone (typically from Kenema and Kailahun districts). It is present but less common in the Central African Republic, Mali, Senegal and other nearby countries, and less common yet in Ghana and the Democratic Republic of the Congo. Benin had its first confirmed cases in 2014, and Togo had its first confirmed cases in 2016.'''

The spread of Lassa outside of West Africa has been very limited historically. Twenty to thirty cases have been described in Europe, cited as being caused by importation through infected individuals. These causes found outside of West Africa were found to have a high fatality risk because of the delay of diagnosis and treatment due to being unaware of the risk associated with the symptoms. These imported cases have not manifested in larger epidemics outside of Africa due to a lack of human to human transmission in hospital settings. The exception of this happened in 2003 when a healthcare worker became infected before the patient showed clear symptoms.

Epidemiological research relating to Lassa Fever is evolving as greater understanding of the disease progress and diagnostic techniques improve. The study of the epidemiology of Lassa fever is complicated by a lengthy incubation period, which may be up to three weeks. Incubation periods as long as Lassa fever may affect spatial clustering of the disease by limiting the understanding of the incidence and distribution of the disease. The spatial clustering for this disease is still in development as a lack of easy-available diagnosis, limited public health surveillance infrastructure, and high clustering of incidence near high intensity sampling make for an incomplete look at the impact of Lassa in this region.